Be sure to bring proof of residency and income. They may ask for your last year's tax form for verification. And a book or other form of time-waster - you'll be waiting a while. (Based on my own experience at the one in our neck of Ohio.)

Oh, and make sure that you schedule a check-up every couple of months on the off-chance a serious problem pops up; the waiting lists between making an appointment and getting an appointment are often a minimum of a month to three months. At least that's how the clinics are here in California.